1. Field of the Invention
The present invention relates to a multilayer resin pipe for an automotive fuel line and, more particularly, to a multilayer resin pipe provided with a conductive resin layer containing carbon nanotubes.
2. Description of the Related Art
Metal pipes have been generally used as fuel pipes on automobiles. Metal pipes are plated or coated with a resin film to enhance the corrosion resistance and chemical resistance thereof.
Recently, resin pipes have been used as well as metal pipes for fuel lines. Resin pipes have many advantages over metal pipes. Resin pipes are not rusted, can be easily processed, are lightweight and increase the degree of freedom of design.
When a fuel pump pumps the fuel from a fuel tank into an automotive fuel line and when the fuel flows through the automotive fuel line, static electricity is generated due to friction between the fuel and the fuel pump and between the fuel and a fuel pipe forming the automotive fuel line and the fuel pipe is charged. The charged fuel pipe produces spark discharges. The spark discharges damage the coating film of the fuel pipe to deteriorate the corrosion resistance and abrasion resistance of the fuel pipe. Therefore, the fuel pipe needs to be connected to a grounded on the automotive body to discharge static electricity from the fuel pipe.
Since the resin pipe is intrinsically dielectric, static electricity tends to accumulate on the resin pipe and the accumulated static electricity is liable to cause troubles. Recently developed electrically conductive pipes are made of a material containing an electrically conductive filler, such as carbon black or carbon fibers. The conductivity of a conventional electrically conductive resin pipe made of a material containing an electrically conductive filler decreases with time and cannot maintain sufficient conductivity.
Recently, a resin pipe to be used as a fuel pipe is required to have a low permeability, namely, a permeation resisting ability, additionally to make difficult the permeation of the fuel through the resin pipe. The low permeability is important to prevent the permeation of the fuel through the fuel pipe and the emission of the fuel into the atmosphere from the viewpoint of environmental protection.
The term “low-permeability resin” is used to indicate resins meeting a quality determined by the following permeability test methods. A CARB DBL method which is carried out by a SHED testing machine is a representative permeability test method of testing resins for fuel pipes.
Referring to FIG. 6, a resin pipe 2 having an inside diameter of 6 mm, an outside diameter of 8 mm and a length of 5 m or above is tested. The opposite ends of the resin pipe 2 are connected by sealing joints 5 to a sealed container 4 made of a stainless steel. The resin pipe 2 filled up with test fuel is held at 40° C. for fifty days or longer for pretreatment. Then, the pretreated resin pipe 2 is connected to a SHED testing machine, not shown. The SHED testing machine measures the quantity of hydrocarbons permeated the resin pipe 2 and contained in the test fuel contained in the resin pipe 2. When the measured quantity of hydrocarbons is 50 mg/m·day or below, the resin forming the resin pipe 2 is called a low-permeability resin.
A conventional multilayer resin pipe designed to meet required a low permeability has an inner layer to be exposed to fuel made of a resin having a low permeability and an outer layer of a polyamide resin or the like covering the inner layer and bonded to the inner layer with an adhesive layer. This conventional multilayer resin pipe, however, does not have both electrical conductivity and low permeability.